Quasi-equilibrium binary black hole initial data for dynamical evolutions

We present a formalism for constructing quasiequilibrium binary black hole initial data suitable for numerical evolution. We construct quasiequilibrium models by imposing an approximate helical Killing symmetry appropriate for quasicircular orbits. We use the sum of two Kerr-Schild metrics as our background metric, thereby improving on conformal flat backgrounds that do not accommodate rotating black holes and providing a horizon-penetrating lapse, convenient for implementing black hole excision. We set inner boundary conditions at an excision radius well inside the apparent horizon and construct these boundary conditions to incorporate the quasiequilibrium condition and recover the solution for isolated black holes in the limit of large separation. We use our formalism both to generate initial data for binary black hole evolutions and to construct a crude quasiequilibrium, inspiral sequence for binary black holes of fixed irreducible mass.